On 2024/6/25 22:16, Waiman Long wrote:
On 6/25/24 10:11, chenridong wrote:
On 2024/6/25 18:10, Michal Koutný wrote:
Hello.
On Tue, Jun 25, 2024 at 11:12:20AM GMT,
chenridong<chenridong@xxxxxxxxxx> wrote:
I am considering whether the cgroup framework has a method to fix this
issue, as other subsystems may also have the same underlying problem.
Since the root css will not be released, but the css->cgrp will be
released.
<del>First part is already done in
d23b5c5777158 ("cgroup: Make operations on the cgroup root_list
RCU safe")
second part is that</del>
you need to take RCU read lock and check for NULL, similar to
9067d90006df0 ("cgroup: Eliminate the need for cgroup_mutex in
proc_cgroup_show()")
Does that make sense to you?
A Fixes: tag would be nice, it seems at least
a79a908fd2b08 ("cgroup: introduce cgroup namespaces")
played some role. (Here the RCU lock is not for cgroup_roots list
but to
preserve the root cgrp itself css_free_rwork_fn/cgroup_destroy_root.
HTH,
Michal
Thank you, Michal, that is a good idea. Do you mean as below?
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index c12b9fdb22a4..2ce0542067f1 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -5051,10 +5051,17 @@ int proc_cpuset_show(struct seq_file *m,
struct pid_namespace *ns,
if (!buf)
goto out;
+ rcu_read_lock();
+ spin_lock_irq(&css_set_lock);
css = task_get_css(tsk, cpuset_cgrp_id);
- retval = cgroup_path_ns(css->cgroup, buf, PATH_MAX,
- current->nsproxy->cgroup_ns);
+
+ retval = cgroup_path_ns_locked(css->cgroup, buf, PATH_MAX,
+ current->nsproxy->cgroup_ns);
css_put(css);
+
+ spin_unlock_irq(&css_set_lock);
+ cgroup_unlock();
+
if (retval == -E2BIG)
retval = -ENAMETOOLONG;
if (retval < 0)
That should work. However, I would suggest that you take
task_get_css() and css_put() outside of the critical section. The
task_get_css() is a while loop that may take a while to execute and
you don't want run it with interrupt disabled.
Cheers,
Longman
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -5050,11 +5050,18 @@ int proc_cpuset_show(struct seq_file *m, struct
pid_namespace *ns,
buf = kmalloc(PATH_MAX, GFP_KERNEL);
if (!buf)
goto out;
-
css = task_get_css(tsk, cpuset_cgrp_id);
- retval = cgroup_path_ns(css->cgroup, buf, PATH_MAX,
- current->nsproxy->cgroup_ns);
+
+ rcu_read_lock();
+ spin_lock_irq(&css_set_lock);
+
+ retval = cgroup_path_ns_locked(css->cgroup, buf, PATH_MAX,
+ current->nsproxy->cgroup_ns);
+
+ spin_unlock_irq(&css_set_lock);
+ rcu_read_unlock();
css_put(css);
+
if (retval == -E2BIG)
retval = -ENAMETOOLONG;
if (retval < 0)
Yeah, that looks good, i will test for a while. I will send a new patch
if no other problem occurs.
Thank you.
Regards,
Ridong
